The Parts of a CSS Rule

All rules, regardless of where they are located or what type they are, have the following three parts:

Selectors are the alpha/numeric characters that identify a rule. The selector can be an HTML tag selector, a class, or an ID.

Properties identify what is being defined. There are several dozen properties, each one responsible for an aspect of the page content's behavior and appearance.

Values are assigned to a property to define its nature. A value can be a keyword such as "yes" or "no," a number, or a percentage. The type of value used depends solely on the property to which it is assigned.